1. Field of the Invention
This invention relates generally to cable television communication systems. More particularly, the invention relates to a cable television communication system which includes an adaptive protocol for remotely upgrading communicating nodes without interrupting system operation.
2. Description of Related Art
Over the last two decades, the availability of cable television (CATV) service to individual homes has increased dramatically. A number of different types of CATV communication systems have evolved to provide a broader array of CATV services. Conventional one-way CATV systems primarily provide video programming services, which are sent over the CATV physical link in a downstream direction, from the headend of a CATV system to a plurality of subscriber units.
Two-way CATV systems have become increasingly standard in the industry as the popularity and diversity services has grown, such as pay per view (current) and interactive banking and home shopping (near future). Two-way CATV systems support both downstream and upstream communication. Accordingly, individual subscribers may communicate with the headend, other subscribers or service providers within the system. These systems also permit subscribers to select specific video programming or consumer services and pay only for those services which are used.
CATV communication systems may be either centralized or decentralized. A centralized system concentrates all communication and service functions at the headend of the system. The disadvantage with the centralized system design is that it requires complete compatibility for equipment design and data formats between the network operator, the service provider and the equipment manufacturer. Further, the centralized network architecture requires complex headend equipment capable of processing all of the different data services simultaneously.
In a decentralized system, the network operator provides the base physical transmission network and a protocol for communication between subscriber units and service providers. Each subscriber unit and each service provider define a separate node within the CATV system. The network operator monitors the status of the system to ensure that the system is operating properly and within established parameters. The network operator also controls which nodes can access the system. A two-way CATV communication system with a decentralized network intelligence is disclosed in U.S. Pat. No. 4,533,948 (McNamara et al.), which is herein incorporated by reference as if fully set forth.
To communicate between CATV nodes, the CATV system uses a communication protocol for data transmission. Protocol syntax processors must also be provided at each node for processing received data in accordance with the specific system protocol. The protocol syntax processor may consist of hardware components or may comprise software that is downloaded into each node. When in receive mode, the processor receives incoming frames of a protocol, which typically comprise a plurality of nested layers of predefined fields. The processor strips off the outermost layer, which contains the information needed to establish the basic communication functions for the incoming frames. The remaining frame components, related to higher level functions, are forwarded for further processing by the node. When in transmit mode the processor adds the functional layer header onto the data to be transmitted, thereby nesting the data within the functional layer. In this manner, the protocol facilitates node to node communications through the CATV system.
Existing CATV communication systems utilize fixed protocol syntax processors designed to process a specific protocol. Each protocol may include a revision field that identifies the protocol version being used by the system. Often, the protocol version is one of the parameters that is negotiated between the functional layers in a server and a client.
The revision field identifies how the frame should be processed, for example, which fields within the frame should be processed by the protocol syntax processor and which may be ignored. The revision field permits the expansion and revision of a protocol. However, any changes made to the protocol are inherently limited in order to maintain compatibility with the existing protocol syntax processor since the protocol syntax processor within each node is fixed.
Existing CATV protocols do not provide for complete replacement of the protocol syntax processor, thereby posing serious limitations on existing CATV systems. When upgrades to the physical transmission network or the protocol are required to employ new technologies or services that may not yet be envisioned, existing protocols may be incompatible with the changes. Accordingly, present system upgrades may require individual installation of completely new protocol syntax processors on each communicating node. This procedure is labor-intensive and cost prohibitive.